Two-piece tire with improved tire tread belt and carcass

ABSTRACT

A two-piece tire assembly has a removable tread belt  12  for installing about the circumference of a tire carcass  14.  The tread belt has a pair of lateral ends each axially extending beyond the inflated unloaded carcass  14  at the circumferential surface by a distance of at least 4% of the width as measured at the tread belt  12  and carcass  14  interface. The carcass  14  has an abrasion resistant rubber layer  82 A at the tread belt interface. The tread belt  12  also has the abrasion resistance tread compound  82 B at the carcass  14  interface.

RELATED APPLICATIONS

[0001] This patent application claims priority to co-pending to U.S.patent application Ser. No. 10/339,199, filed Jan. 9, 2003, a divisionof U.S. patent application Ser. No. 09/840,385, filed Apr. 23, 2001,currently pending.

TECHNICAL FIELD

[0002] This invention relates to pneumatic tires with tread belts andmore particularly to an improved removable tread belt pneumatic tireconstructed of a removable tread belt mounted on a radially reinforcedbeaded tire carcass that is typically for use with earthmoving vehicles.

BACKGROUND OF THE INVENTION

[0003] The tread belt pneumatic tires of the present invention aregenerally designed for use on large eartbmover vehicles and aresubjected to high stress and loads under harsh environmental conditionssuch as in rock quarries, mines, foundries, and other areas where tiresare subjected to puncture-producing and wear-inducing conditions.

[0004] As discussed in U.S. Pat. No. 4,351,380, certain prior art treadbelt tire assemblies comprise a plurality of ground-engaging shoesspaced about the periphery of the supporting structure. The heavy loadson the shoes result in great stresses being developed that sometimeslead to premature tire failure. The U.S. Pat. No. 4,351,380 patent isdirected to an improved track belt assembly which comprise a pluralityof shoes spaced about the periphery of a load-supporting structure andsecured to a reinforcing belt structure disposed on the side of the shoeopposite the ground-engaging side thereof.

[0005] The large pneumatic tires, which are typically used forearthmoving vehicles, sometimes fail due to the high stress and loadscaused by the harsh environmental conditions in which they are operated.These large prior art pneumatic tires had a greater tendency to fail inone of three tire locations or areas. The first problem area was thatthe turn-up end of the ply would sometimes break through the sidewall ofthe tire. A second problem area was a tire failure in the bead area. Thethird problem area was a tendency to fail in the crown and/or shoulderarea of the tire.

[0006] In the prior art, conventional solutions to these problemsinclude increasing the gauge of the sidewall to increase the bendingstiffness, increasing bead area stiffness and robustness, and decreasingtire deformation under load by increasing the sidewall stiffness. Tofurther improve tire durability, the ply turn-up portion of tires wastypically reinforced.

[0007] In U.S. Pat. No. 4,609,023, having a common assignee with thepresent invention, the sidewall inserts were incorporated in the tirecarcass to allow the ply structure to conform to its natural shape whenthe tire is inflated.

[0008] The most relevant prior art patent, U.S. Pat. No. 4,050,495,issued Sep. 27, 1977, teaches the use of a removable tread beltinstalled as an annular belt about the circumference of a tire carcass.The tread belt included laterally extending bars encapsulated in amatrix of rubber. The ends of the bars extended outwardly to a pointbeyond the widest portion of the carcass sidewall. The tread belt wasrigidly supported by the bars at the ends of the tread belt to preventdeflection of the overhanging and otherwise unsupported tread belt atthe lateral ends.

[0009] With the continual drive to improve earthmover performance, thereis a continuing need to provide novel methods and tire designs forimproving earthmover tire durability. The present invention is directedto an improved pneumatic tire and removable tread belt assembly withwhich the frequency of premature tire failure is thought to besubstantially reduced. The present invention is also directed toproviding an improved pneumatic tire and tread belt assembly which isdesigned to allow large tires to be transported in several sections andthen assembled at the construction site to ease the otherwise difficultproblem of transporting the large tires, i.e. sometimes over 13 feet inheight and approximately 8,000 to 15,000 pounds. Moreover, the presentinvention relates to an improved pneumatic tire and removable tread beltassembly with which the driving characteristics of the tire can be moreeconomically changed and the inventory of the number of tire spares thatare typically needed can be reduced.

OBJECTS AND SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to provide a pneumatictire for an earthmover vehicle, the pneumatic tire being as defined inone or more of the appended claims and, as such, having the capabilityof being constructed to accomplish one or more of the followingsubsidiary objects.

[0011] It is another object of the present invention to provide animproved tire and removable tread belt assembly for an earthmovervehicle wherein the frequency of premature tire failure has beensubstantially reduced.

[0012] Another object of the present invention is directed to providingan improved tire and removable tread belt assembly which is designed toallow large tires to be transported in several sections and thenassembled at the delivery site.

[0013] Still another object of the present invention is to provide animproved tire and removable tread belt assembly with which the drivingcharacteristics of the tire can be quickly and economically changed.

[0014] Yet another object of the present invention is to provide animproved tire and removable tread belt assembly with which the number oftire spares that are stored in inventory can be reduced.

[0015] Still another object of the present invention is to provide animproved tire and removable tread belt assembly with a unique tread beltthat is restrained from expanding radially outwardly.

[0016] A further object of the present invention is to provide animproved tire and removable tread belt assembly wherein the tire treadswill maintain a more flat tread profile which will improve tread lifeand durability.

[0017] A still further object of the present invention is to provide animproved tire and removable tread belt assembly wherein the belt isconstructed to provide penetration protection.

[0018] In accordance with an embodiment of the invention a two-piecetire assembly is disclosed. The two-piece tire assembly has a removabletread belt for installing about the circumference of a tire carcass anda tire carcass having an inflated and unloaded outer circumferentialsurface having an axial dimension no greater than the axial width of theremovable tread belt.

[0019] The tread belt has a pair of lateral ends each axially extendingbeyond the inflated unloaded carcass at the circumferential surface by adistance of at least 4% of carcass width as measured at the tread beltand carcass interface, and wherein the tread belt width is at leastequal to or wider than the loaded deflected carcass width as measured atthe outer circumferential surface of the carcass.

[0020] Each lateral end of the tread belt has a plurality ofcircumferentially extending substantially zero degree oriented cords ina first reinforcement layer and is radially inwardly flexible underload.

[0021] The tread belt preferably has a radially outer surface having asubstantially flat tread arc radius R₁ between the lateral endsextending from 50% to 75% of the tread belt axial width and a smallertread arc radius R₂ extending from each of the lateral ends to the firsttread arc R₁, the radially outer tread surface having a sloping surfaceextending from a tangency to R₂ to a lateral end. The radial differencein the tread belt surface as measured at the centerline of the treadbelt and each lateral end of the removable tread belt is greater than0.3% of the outside diameter as measured at the centerline of the treadbelt.

[0022] The tread belt has a belt reinforcing structure radially outwardof the circumferentially extending cords in the first reinforcementlayer. The belt reinforcing structure has a pair of cross-plies and aradially outer ply having cords oriented substantially 90 relative tothe circumferentially extending cords in a first reinforcement layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a cross-sectional view illustrating the two-piece tirewith a removable tire tread belt mounted on an inflatable tire carcassand made in accordance with the present invention;

[0024]FIG. 2 is an enlarged, cross-sectional view illustrating one sideor half of the symmetrical tire shown in FIG. 1 and made in accordancewith the present invention; and

[0025]FIG. 3 is an enlarged, cross-sectional view illustrating the beadarea of the tire shown in FIG. 2.

DEFINITIONS

[0026] “Apex” means a non-reinforced elastomer positioned radially abouta bead core.

[0027] “Aspect ratio” of the tire means the ratio of its section height(SH) to its section width (SW) multiplied by 100% for expression as apercentage.

[0028] “Axial” and “axially” mean lines or directions that are parallelto the axis of rotation of the tire.

[0029] “Bead” means that part of the tire comprising an annular tensilemember wrapped by the ply cords and shaped, with or without otherreinforcement elements such as flippers, chippers, apexes, toe guardsand chafers, to fit the design rim.

[0030] “Belt or breaker reinforcing structure” means at least two layersof plies of parallel cords, woven or unwoven, underlying the tread,unanchored to the bead, and having both left and right cord angles inthe range from 17° to 75° with respect to the equatorial plane of thetire.

[0031] “Bias ply tire” means a tire having a carcass with reinforcingcords in the carcass ply extending diagonally across the tire from beadcore to bead core at about 25 -50 angle with respect to the equatorialplane of the tire. Cords run at opposite angles in alternate layers.

[0032] “Circumferential” means lines or directions extending along theperimeter of the surface of the annular tread perpendicular to the axialdirection.

[0033] “Chafers” refers to narrow strips of material placed around theoutside of the bead to protect cord plies from degradation and chaffingcaused by movement of the rim against the tire.

[0034] “Chippers” means a reinforcement structure located in the beadportion of the tire.

[0035] “Cord” means one of the reinforcement strands of which the pliesin the tire are comprised.

[0036] “Equatorial plane (EP)” means the plane perpendicular to thetire's axis of rotation and passing through the center of its tread.

[0037] “Flipper” means a reinforced fabric wrapped about the bead coreand apex.

[0038] “Footprint” means the contact patch or area of contact of thetire tread with a flat surface under load and pressure.

[0039] “Inner liner” means the layer or layers of elastomer or othermaterial that form the inside surface of a tubeless tire and thatcontain the inflating gas or fluid within the tire.

[0040] “Net-to-gross ratio” means the ratio of the tire tread rubberthat makes contact with the road surface while in the footprint, dividedby the area of the tread in the footprint, including non-contactingportions such as grooves.

[0041] “Nominal rim diameter” means the diameter of the rim base at thelocation where the bead of the tire seals.

[0042] “Normal inflation pressure” refers to the specific designinflation pressure at a specific load assigned by the appropriatestandards organization for the service condition for the tire.

[0043] “Normal load” refers to the specific load at a specific designinflation pressure assigned by the appropriate standards organizationfor the service condition for the tire.

[0044] “Ply” means a continuous layer of rubber-coated parallel cords.

[0045] “Radial” and “radially” mean directions extending radially towardor away from the axis of rotation of the tire.

[0046] “Radial-ply tire” means a belted or circumferentially-restrictedpneumatic tire in which the ply cords which extend from bead to bead arelaid at cord angles between 65 and 90 with respect to the equatorialplane of the tire.

[0047] “Section height (SH)” means the radial distance from the nominalrim diameter to the outer diameter of the tire at its equatorial plane.

DETAILED DESCRIPTION OF THE INVENTION

[0048] With reference to FIG. 1, there is illustrated a cross-section ofa two-piece pneumatic tire 10 which in the specific exemplary embodimentillustrated is a size 33.00R51 earthmover tire. At an inflation pressureof 102 psi the size 33.00R51 tire has a 119.9 inch (303 cm) maximuminflated outside diameter, a 37.2 inch (94 cm) maximum inflated widthtire in the axial directions, and a nominal bead diameter of 51.00inches (130 cm). The tires are typically inflated to a pressure of about100 pounds per square inch (psi) with air and sometimes with anair/nitrogen mixture.

[0049] The improved tread belt pneumatic tire 10 includes a groundengaging, circumferentially extending tread belt 12 mounted on aradially reinforced, beaded tire carcass 14. The beaded tire carcass 14generally includes a pair of tire sidewalls 16, 18 extending radiallyinwardly from the outer circumferential surface 20 of the tire carcassand terminating at their radial extremities in a pair of bead wires 22,24, respectively. The sidewalls 16, 18 each have an upper portion 16 a,18 a, respectively, in the shoulder region of tire carcass 14 andradially inward of the maximum section width of the tire carcass, and alower portion 16 b, 18 b, respectively, adjacent the bead wires 22, 24,respectively, and radially inward of the maximum section width of thetire carcass 14. The details of the construction of tire carcass 14 aredescribed in detail hereinafter.

[0050] Tire Carcass

[0051] Referring FIGS. 1 and 2, the details of tire carcass 14 areillustrated. The axially inward surface 28 is an inner ply liner 26which forms an innerliner that holds the air pressure for inflating tire10. The inner ply liner 26 covers the entire interior facing surface 28of the tire carcass 14 and serves to hold the air within the carcassthat is used to inflate tire 10. Fabric barrier plies 30 and 32 areprovided within the tire carcass 12 in the area of the curved portion ofinterior surface 28 to provide support for the upper portion of thebarrier rubber layer 36 and prevent the barrier rubber from beingsqueezed through the ply wires in the ply layer 34. While two barrierplies 30 and 32 are illustrated, it is within the terms of the inventionto use between zero and four barrier plies, as needed for a specificdesign.

[0052] The carcass 14 also includes in its construction at least onerubberized laminated ply layer 34 of tire cord fabric which extendsradially inwardly from the outer circumferential surface 20 of the tirecarcass, also called the crown area of the tire carcass, and has turnupends 34 a and 34 b which wrap or loop around bead wires 22 and 24,respectively. Although the carcass ply 34 is shown as being of singleply construction, a multi-ply construction can be employed if desired.Preferably, the carcass ply 34 is made of a rubberized ply of steelcord, but it can be made of a non-steel carcass reinforcing material.

[0053] At the radially outermost portion of the carcass 14 there is athin layer of abrasion resistant tread compound 82A. The abrasionresistant tread compound 82A forms a tough durable long wearing surfacebetween the tread belt 12 and the carcass 14. The use of tread rubber isan ideal material because it is adapted to form grooves and ridges or asshown in FIGS. 1 and 2, the lands 76 and grooves 78, which are used toretain the belts.

[0054] Between the innerliner 26 and the ply layer 34 is a barrierrubber layer 36 which backs up the entire length of ply layer 34 and isformed of a soft compound of rubber which squeezes against the ply layer34. Annular stiffeners, known as apexes or apex elements 38, 39 herein,each having a generally triangular shape are provided radially outwardof the bead wires 22, 24, respectively, and between the barrier rubber36 and the innerliner 26. The apexes 38, 39 extend from approximatelythe mid-sidewall and the area of innerliner 26 radially outward from thebead wires 22, 24, respectively, for stiffening the bead area to helpprevent the tire from bending over the flange 35. Axially outward fromapexes 38, 39 and between the ply layer 34 where it turns up about beadwires 22,24 are located lower gum chafers 40, 41, respectively, thatsupport the bead wires 22, 24, respectively, in the area of the wheelmounting rim 42 and to prevent chafing of the tire by an adjacent wheelmounting rim. Upper gum chafers 44, 45 are disposed against the lowergum chafers 40, 41, respectively, and the lower tire sidewalls 16 b, 18b, respectively, to provide support for the bead wires 22, 24 in thearea of the flange 35 and to prevent chafing of the tire by an adjacentwheel mounting rim.

[0055] Between the lower chafers 40, 41 and the rubber barrier 36 in thearea partially surrounding bead wires 22, 24 are located fabric or wirechafer plies 46, 47 that support the bead wires 22, 24, respectively. Asbest seen in FIGS. 2 and 2A, the chafer plies 46 are primarily disposedagainst the inner facing surfaces of lower chafers 40, 41. Between theinner surface of ply layer 34 and the bead wires 22 and 24 are locatedflippers 48, 49, respectively, which are reinforced fabric materialsthat are wrapped about the bead core and at least a portion of one ofthe apexes. On either side of the ends 34 a, 34 b of ply layer 34 aretwo wire coat, gum layers 50 and 52 which cover the ends 34 a, 34 b,respectively, of ply 34 and enable the movement of ply 34 between thegum layers 50 and 52 without exposing the wire within ply 34 during tireconstruction or severe bending of the tire.

[0056] Apex Configuration

[0057] Two annular stiffeners, referred to as apexes 54, 55 herein, eachhaving a generally four sided shape, are provide radially outward of thebead wires 22, 24, respectively, between flippers 48, 49, and out toapexes 58, 59, for stiffening the area about the bead wires 22, 24,respectively, to help prevent the tire from bending over the flange 35.The apexes 54, 55 are further disposed between the lower inner end ofrubberized ply layer 34 and the turn-up ends 34 a and 34 b. Abuttedagainst and extending radially outward from the apexes 54 and 55 are twoannular stiffeners, referred to herein as apexes 58 and 59,respectively, which help support the ends 34 a and 34 b of rubberizedply layer 34. The apexes 54, 55, are constructed of a relatively hardcompound having a modulus of about 12.2-14.9 megapascals/cm² at 200%elongation. Axially outward from the apexes 58 and 59 are the outerapexes 62 and 64, respectively. The apexes 38, 39, 58, 59, and 62, 64are generally constructed of the same relatively soft rubber compoundhaving a modulus of about 7.2-8.8 megapascals/cm² at 200% elongation andact to provide a soft cushion that absorbs the stresses around the turnup ends 34 a and 34 b of the ply layer 34 which is caused by stressforces generated by the flexing of the tire. While the apexes 38, 39,58, 59, and 62, 64 are typically constructed of the same rubbercompound, it is within the terms of the invention to construct one ormore of the apexes with a different modulus within the range of betweenabout 7.2 and 8.8 megapascals/cm² at 200%. In the preferred embodiment,the apexes 38, 39, 58, 60, 62 and 64 are softer than the apexes 54 and55 which are located directly adjacent and radially outward from thebead wires 22 and 24, respectively. Preferably the rubber compound usedto form the apexes 54 and 55 are about 20% to about 50%, and preferablyabout 20% to about 50% stiffer than the rubber compound used to formapexes 38, 39, 58, 59, 62 and 64.

[0058] The location of the ply turn-up ends 34 a and 34 b are animportant aspect of the carcass design. As best illustrated in FIG. 3,preferably the turn-up ends 34 a, 34 b are located radially outward adistance of between about 2 and 3 bead diameters from the intersectionof a centerline 66 which extends through the center of bead wires 22, 24and a line 67 which is tangent to the most radially inward surface ofthe carcass ply 34 where the carcass ply portions 34 a, 34 b loop aroundthe wire beads 22, 24 to a line 68 which is perpendicular to centerline66 and is tangent to the outer end of the ply layer 34. This location ofthe outer ends of the turn-up ends 34 a, 34 b of ply layer 34 isimportant in that it can withstand the pressure exerted against the plyend, which was sometimes sufficient to cause the ply end to breakthrough the sidewall in prior art constructions where the turn-up endsextend closer to the center of the tire sidewalls. The advantage ofhaving the outer ends of the turn-up ends 34 a, 34 b of carcass ply 34at a lower position closer to the radial outward portion of the flange35 is so that when operating conditions cause the tire to deflectoutwards, the ends of turn-up ends 34 a, 34 b of the ply layer 34 willbe supported by flange 35. This arrangement will greatly reduce thepossibility that the outer ends of turn-up ends 34 a, 34 b will be thecause of a crack in or penetrate axially outward through the sidewall ofthe tire carcass 14.

[0059] The ply line of ply layer 34 follows the natural ply line, whichmeans it is already at its natural shape upon inflation. The carcass ply34 retains its natural shape when inflated to reduce the inflationstrain on the tire. The portion of the ply cord extending down to thebead 22 is equally supported along its length by the axially interiorsurface 37 of the rim flange 35 which is substantially parallel to thecenterline 66 passing though beads 22, 24.

[0060] Tread Belt

[0061] The ground engaging, circumferentially extending tread belt 12 isremovably mounted onto the tire carcass 14. As best shown in FIG. 2, theunderside or inner circumference surface 70 of tread belt 12 comprises aplurality of annular lands 72 and grooves 74 that mate with lands 76 andgrooves 78 of tire carcass 14 to restrain belt 12 from lateral or axialmovement with respect to the carcass 14. The tire tread belt 12 includesa tread portion 80 and a plurality of tread belts 84, 86, and 88(84-88). A radially inner belt layer 84 and 86 have cords of steelhaving a core strand surrounded by sheath strands. The core strandpreferably has a plurality of three filaments forming the core. The wireconstruction is as described in co-pending application Ser. No.09/507,316, filed Feb. 18, 2000, entitled STEEL CORD FOR REINFORCINGELASTOMERIC ARTICLES which is incorporated by reference herein in itsentirety. Each tread belt layer 84, 86 has the cords oriented at anangle of 15° to 80° relative to the circumferential direction and spacedat 4 ends per inch. These adjacent layers 84, 86 being equal butoppositely oriented.

[0062] At the radially innermost portion of the tread belt 12 there is athin layer of abrasion resistant tread compound 82B. The abrasionresistant tread compound 82B forms a tough durable long wearing surfacebetween the tread belt 12 and the carcass 14. The use of tread rubber isan ideal material because it is adapted to form grooves and ridges or asshown in FIGS. 1 and 2, the lands 76 and grooves 78, which are used toretain the belts. In order to avoid exposure of the wires 92 upon wearof the abrasion resistant tread compound 82B, the thickness or gauge ofthe abrasion resistant tread compound 82B is generally at least 0.1inches in the region of the grooves 78. In another embodiment, thethickness is at least 0.3 inches. The thickness or gauge in the regionof the lands 76 is equal to the thickness in the region of the groove 78plus the height of the land 76.

[0063] The radially outermost third layer 88 has the steel cordsoriented at 90° relative to the circumferential direction. This incombination with the belt layers 84, 86 creates a very strongconstruction. Radially inward of these belt reinforcement layers is aunique first reinforcement layer 90 having cords 92 oriented 0° relativeto the circumferential direction, preferably spaced at 3 EPI.

[0064] While three tread belts 84-88 are illustrated, it is within thescope of the invention to use other numbers of tread belt layers asneeded. The combination of a removable tire tread belt 12 with a tirecarcass 14 for use with large earthmoving vehicles is important in thatit enables a portion of a tire 10 to be replaced instead of the entiretire in the event that one portion of the tire, i.e., the tire belt 12or the tire carcass 14, wears out before the other part. Also, it may bedesirable to have different types of tread designs such as, for example,driving or steering tread designs. This feature allows for a lessexpensive means of changing the tire tread to construct the appropriatestyle of desired tire. This feature would greatly reduce the cost ofstoring spare tires and could even extend the operating time of thetires.

[0065] A unique aspect of the present invention is the provision of zerodegree wires 92 in the first reinforcement layer 90. The zero degreewires in layer 90 encircle the tire tread belt 12 and are provided torestrict the radially outward growth of the tread belt 12 due to aserious deflection in the tire carcass. By keeping the tire tread belt12 from expanding radially outward, the tire's tread will maintain amore flat tread profile which will improve tread life and durability.The zero degree 92 wires in first reinforcement layer 90 eliminate theneed for a larger number of belt layers.

[0066] With particular reference to the first reinforcement layer 90 itis believed most beneficial to have the axially outermost cords 92axially inward of the lateral ends of the belt layers 84 and 86. Asshown the lateral ends of the belt layer 84 overhang the adjacent firstreinforcement layer 90 and project axially outward from the lateral endsof belt layer 86. By insuring the belt layers 84 and 86 overhang orextend beyond the zero degree cords 92 of the first reinforcement layer90 provides added protection against cut damage of the cords 92. As canbe easily appreciated as a large sharp rock is rolled over in the pathof the tread belt, the lateral ends of the tread belt can deflect andthe belt layers 84, 86 by overhanging actually can bend over the zerodegree cords 92 stopping the rock from cutting those cords.

[0067] The primary advantage of the tread belt design in the region ofthe lateral edges is the fact that the lateral edge portions of thetread belt 12 at the surface adjoining the circumferentially outersurface of the carcass 14 extend beyond the carcass 14 as shown at theinterface 20 of the tread belt 12 and the carcass 14. This increases theflexibility of the tread belt 12 and improves the handlingcharacteristics of the tire 10. The outer surface of the tread has aninclination of θ, θ being about 4° slope in the lateral portions of thetread and is flat or 0° sloped in the central region. The flat shapedcentral region extends at least 50% of the total tread width. In the31.00R51 design, the central portion extends over 9.00 inches and eachlateral portion extends from the central portion 25% or less of thetotal tread width, or about 7.00 inches in the 31.00R51 tire size of thepreferred embodiment tire.

[0068] This transition of the tread surface in the region Lo fromsloping flat 0° to a 4° radially inward slope creates a shoulderdrop-off (D) of at least 10 mm. This feature lowers the tread belt 12contact pressure in the lateral portions and this generally reduces theshoulder wear particularly in the steering wheel positions. An addedbenefit is noted in that the deflection of the lateral portion isenhanced by a reduction in the radial height of the tread created by theshoulder drop-off (D). This means that the thinner tread at the lateralends is easier to deflect radially outwardly but almost paradoxicallythe amount of inward pressuring trying to deflect inwardly the treadedge is lowered by the sloping shoulder. In combination this insuresthat while the tread belt is deliberately made flexible at the lateraledge to accommodate large stones and rock, preferably, the entirecentral region of the tread has even footprint pressures at the crownwherein the tread is fully supported. Ideally, the footprint pressure atthe shoulders of the tread are equal to, or slightly less than, thecentral region.

[0069] At the interface between the carcass 14 and the tread belt 12 itis believed important that the tread belt 12 overhangs the inflated andunloaded carcass by an amount of at least 15 mm or 4% of the carcasswidth as measured at the interface 20. As the tire 10 is placed undernormal load the carcass 14 expands radially outwardly to a locationalmost aligned with the lateral end of the tread belt 12. It is believedundesirable to have the carcass 14 at the tread belt 12 interface to beextending laterally outward of the tread belt 12. The subtle relativemovement of the tread belt 12 to the carcass 14 means that to insure thecarcass 14 is not exposed requires the tread belt 12 to actuallyoverhang the carcass 14 at the interface. While large amounts ofoverhang may be feasible it is considered inefficient to allow the treadbelt 12 to extend beyond the maximum section width of the carcass. Thisis true for several reasons, first being each 1 inch of axial tread beltwidth on large sized tires such as 33.00R51 tire weighs approximately100 lbs., secondarily the tread thickness is about 5.00 inches orgreater and the distance to a location of the maximum section width ofthe carcass is another 24 inches meaning the rocks and debris mostlikely to damage the carcass 14 will strike at the tread belt interface.Rocks 30 inches or greater simply are too unlikely to be traversable inthe quarry and therefore create no realistic threat to carcass damage,thirdly because the present invention has the lateral edges to be of areduced stiffness to facilitate some degree of deflection radiallyinwardly, too large of an overhang could lead to flexure fatigue in thefirst reinforcement layer 90 requiring stiffening of the tread belt aswas done in the prior art patent U.S. Pat. No. 4,050,495.

[0070] It is apparent that there has been provided in accordance withthis invention apparatus and methods for constructing an improved tire10 and removable tread belt assembly wherein the tire durability hasbeen substantially increased by the inclusion of an improved apexconstruction. The improved tire and removable track belt assembly allowlarge tires to be transported in several sections and then assembled atthe delivery site. Further, the removable tread belt assembly allows adifferent tread belt 12 to be applied to a tire carcass 14 so as toalter the driving characteristics of the tire quickly and economically.

[0071] The abrasion resistant tread compound 82A,B may comprise betweenabout 50 and about 100 parts by weight of natural or syntheticpolyisoprene. The component may also include between about 0 and about20 parts by weight of polybutadiene and 0 to about 50 phr ofstyrene-butadiene rubber, to make up a total 100 parts by weight ofelastomer.

[0072] Other elastomers that may be used along with the natural orsynthetic polyisoprene in the abrasion resistant tread compound 82A,Bmay include various general purpose elastomers as are known in the art.The phrase “rubber or elastomer containing olefinic unsaturation” isintended to include both natural rubber and its various raw and reclaimforms as well as various synthetic rubbers. In the description of thisinvention, the terms “rubber” and “elastomer” may be usedinterchangeably, unless otherwise prescribed. The terms “rubbercomposition”, “compounded rubber” and “rubber compound” are usedinterchangeably to refer to rubber which has been blended or mixed withvarious ingredients and materials, and such terms are well known tothose having skill in the rubber mixing or rubber compounding art.Representative synthetic polymers are the homopolymerization products ofbutadiene and its homologues and derivatives, for example,methylbutadiene, dimethylbutadiene and pentadiene as well as copolymerssuch as those formed from butadiene or its homologues or derivativeswith other unsaturated monomers. Among the latter are acetylenes, forexample, vinyl acetylene; olefins, for example, isobutylene, whichcopolymerizes with isoprene to form butyl rubber; vinyl compounds, forexample, acrylic acid, acrylonitrile (which polymerize with butadiene toform NBR), methacrylic acid and styrene, the latter compoundpolymerizing with butadiene to form SBR, as well as vinyl esters andvarious unsaturated aldehydes, ketones and ethers, e.g., acrolein,methyl isopropenyl ketone and vinylethyl ether. Specific examples ofsynthetic rubbers include neoprene (polychloroprene), polybutadiene(including cis-1,4-polybutadiene), polyisoprene (includingcis-1,4-polyisoprene), butyl rubber, halobutyl rubber such aschlorobutyl rubber or bromobutyl rubber, styrene/isoprene/butadienerubber, copolymers of 1,3-butadiene or isoprene with monomers such asstyrene, acrylonitrile and methyl methacrylate, as well asethylene/propylene terpolymers, also known as ethylene/propylene/dienemonomer (EPDM), and in particular, ethylene/propylene/dicyclopentadieneterpolymers. Additional examples of rubbers which may be used include acarboxylated rubber, silicon-coupled and tin-coupled star-branchedpolymers. The preferred rubber or elastomers are polybutadiene and SBR.

[0073] In one aspect, the rubber to be combined with the natural orsynthetic polyisoprene in the abrasion resistant tread compound 82A,B ispreferably one or more diene-based rubbers. For example, one or morerubbers is preferred such as styrene/isoprene/butadiene rubber, emulsionand solution polymerization derived styrene/butadiene rubbers, cis1,4-polybutadiene rubbers and emulsion polymerization preparedbutadiene/acrylonitrile copolymers.

[0074] The abrasion resistant tread compound 82A,B may include fromabout 10 to about 100 phr of a filler selected from carbon black andsilica. Alternatively, the abrasion resistant tread compound 82A,B mayinclude from about 30 to about 70 phr of a filler selected from carbonblack and silica.

[0075] The commonly-employed siliceous pigments which may be used in theabrasion resistant tread compound 82A,B include conventional pyrogenicand precipitated siliceous pigments (silica), although precipitatedsilicas are preferred. The conventional siliceous pigments preferablyemployed in this invention are precipitated silicas such as, forexample, those obtained by the acidification of a soluble silicate,e.g., sodium silicate.

[0076] Such conventional silicas might be characterized, for example, byhaving a BET surface area, as measured using nitrogen gas, preferably inthe range of about 40 to about 600, and more usually in a range of about50 to about 300 square meters per gram. The BET method of measuringsurface area is described in the Journal of the American ChemicalSociety, Volume 60, Page 304 (1930).

[0077] The conventional silica may also be typically characterized byhaving a dibutylphthalate (DBP) absorption value in a range of about 100to about 400, and more usually about 150 to about 300.

[0078] The conventional silica might be expected to have an averageultimate particle size, for example, in the range of 0.01 to 0.05 micronas determined by the electron microscope, although the silica particlesmay be even smaller, or possibly larger, in size.

[0079] Various commercially available silicas may be used, such as, onlyfor example herein, and without limitation, silicas commerciallyavailable from PPG Industries under the Hi-Sil trademark withdesignations 210, 243, etc; silicas available from Rhodia, with, forexample, designations of Z1165MP and Z165GR and silicas available fromDegussa AG with, for example, designations VN2 and VN3, etc.

[0080] Commonly-employed carbon blacks can be used as a conventionalfiller in the abrasion resistant tread compound 82A,B. Representativeexamples of such carbon blacks include N110, N121, N220, N231, N234,N242, N293, N299, S315, N326, N330, N332, N339, N343, N347, N351, N358,N375, N539, N550, N582, N630, N642, N650, N683, N754, N762, N765, N774,N787, N907, N908, N990 and N991. These carbon blacks have iodineabsorptions ranging from 9 to 145 g/kg and DBP number ranging from 34 to150 cm³/100 g.

[0081] It may be preferred to have the abrasion resistant tread compound82A,B to additionally contain a conventional sulfur-containingorganosilicon compound. Examples of suitable sulfur-containingorganosilicon compounds are of the formula:

Z-Alk-Sn-Alk-Z   I

[0082] in which Z is selected from the group consisting of

[0083] where R₆ is an alkyl group of 1 to 4 carbon atoms, cyclohexyl orphenyl; R₇ is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8carbon atoms; Alk is a divalent hydrocarbon of 1 to 18 carbon atoms andn is an integer of 2 to 8.

[0084] Specific examples of sulfur-containing organosilicon compoundswhich may be used in the abrasion resistant tread compound 82A,Binclude: 3,3′-bis(trimethoxysilylpropyl) disulfide, 3,3′-bis(triethoxysilylpropyl) disulfide, 3,3′-bis(triethoxysilylpropyl)tetrasulfide, 3,3′-bis(triethoxysilylpropyl) octasulfide,3,3′-bis(trimethoxysilylpropyl) tetrasulfide,2,2′-bis(triethoxysilylethyl) tetrasulfide,3,3′-bis(trimethoxysilylpropyl) trisulfide,3,3′-bis(triethoxysilylpropyl) trisulfide,3,3′-bis(tributoxysilylpropyl) disulfide,3,3′-bis(trimethoxysilylpropyl) hexasulfide,3,3′-bis(trimethoxysilylpropyl) octasulfide,3,3′-bis(trioctoxysilylpropyl) tetrasulfide,3,3′-bis(trihexoxysilylpropyl) disulfide,3,3′-bis(tri-2″-ethylhexoxysilylpropyl) trisulfide,3,3′-bis(triisooctoxysilylpropyl) tetrasulfide,3,3′-bis(tri-t-butoxysilylpropyl) disulfide, 2,2′-bis(methoxy diethoxysilyl ethyl) tetrasulfide, 2,2′-bis(tripropoxysilylethyl) pentasulfide,3,3′-bis(tricyclonexoxysilylpropyl) tetrasulfide,3,3′-bis(tricyclopentoxysilylpropyl) trisulfide,2,2′-bis(tri-2″-methylcyclohexoxysilylethyl) tetrasulfide,bis(trimethoxysilylmethyl) tetrasulfide, 3-methoxy ethoxy propoxysilyl3′-diethoxybutoxy-silylpropyltetrasulfide, 2,2′-bis(dimethylmethoxysilylethyl) disulfide, 2,2′-bis(dimethyl sec.butoxysilylethyl)trisulfide, 3,3′-bis(methyl butylethoxysilylpropyl) tetrasulfide,3,3′-bis(di t-butylmethoxysilylpropyl) tetrasulfide, 2,2′-bis(phenylmethyl methoxysilylethyl) trisulfide, 3,3′-bis(diphenylisopropoxysilylpropyl) tetrasulfide, 3,3′-bis(diphenylcyclohexoxysilylpropyl) disulfide, 3,3′-bis(dimethylethylmercaptosilylpropyl) tetrasulfide, 2,2′-bis(methyldimethoxysilylethyl) trisulfide, 2,2′-bis(methylethoxypropoxysilylethyl) tetrasulfide, 3,3′-bis(diethylmethoxysilylpropyl) tetrasulfide, 3,3′-bis(ethyl di-sec.butoxysilylpropyl) disulfide, 3,3′-bis(propyl diethoxysilylpropyl)disulfide, 3,3′-bis(butyl dimethoxysilylpropyl) trisulfide,3,3′-bis(phenyl dimethoxysilylpropyl) tetrasulfide, 3-phenylethoxybutoxysilyl 3′-trimethoxysilylpropyl tetrasulfide,4,4′-bis(trimethoxysilylbutyl) tetrasulfide,6,6′-bis(triethoxysilylhexyl) tetrasulfide,12,12′-bis(triisopropoxysilyl dodecyl) disulfide,18,18′-bis(trimethoxysilyloctadecyl) tetrasulfide, 18,18′-bis(tripropoxysilyloctadecenyl) tetrasulfide,4,4′-bis(trimethoxysilyl-buten-2-yl) tetrasulfide,4,4′-bis(trimethoxysilylcyclohexylene) tetrasulfide,5,5′-bis(dimethoxymethylsilylpentyl) trisulfide,3,3′-bis(trimethoxysilyl-2-methylpropyl) tetrasulfide,3,3′-bis(dimethoxyphenylsilyl-2-methylpropyl) disulfide.

[0085] The preferred sulfur containing organosilicon compounds for usein the abrasion resistant tread compound 82A,B are the3,3′-bis(trimethoxy or triethoxy silylpropyl) sulfides. The mostpreferred compounds are 3,3′-bis(triethoxysilylpropyl) disulfide and3,3′-bis(triethoxysilylpropyl) tetrasulfide. Therefore, as to formula I,preferably Z is

[0086] where R₇ is an alkoxy of 2 to 4 carbon atoms, with 2 carbon atomsbeing particularly preferred; alk is a divalent hydrocarbon of 2 to 4carbon atoms with 3 carbon atoms being particularly preferred; and n isan integer of from 2 to 5 with 2 and 4 being particularly preferred.

[0087] The amount of the sulfur-containing organosilicon compound offormula I in the abrasion resistant tread compound 82A,B will varydepending on the level of other additives that are used. Generallyspeaking, the amount of the compound of formula I will range from 0.5 to20 phr. Preferably, the amount will range from 1 to 10 phr.

[0088] The abrasion resistant tread compound 82A,B may contain one ormore heat reactive resin systems to improve tear resistance. Such heatreactive resins may include those comprising a “methylene donor” and a“methylene acceptor”. The term “methylene acceptor” is known to thoseskilled in the art and is used to describe the reactant to which themethylene donor reacts to form what is believed to be a methylolmonomer. The condensation of the methylol monomer by the formation of amethylene bridge produces the resin. The initial reaction thatcontributes the moiety that later forms into the methylene bridge is themethylene donor wherein the other reactant is the methylene acceptor.Representative compounds which may be used as a methylene acceptor areresorcinol, unmodified phenol novolak resins, modified phenol novolakresin, resorcinol novolak resins and mixtures thereof. Examples ofmodified phenol novolak resins include cashew nut oil modified phenolnovolak resin, tall oil modified phenol novolak resin and alkyl modifiedphenol novolak resin.

[0089] The amount of methylene acceptor that is included in the abrasionresistant tread compound 82A,B may vary depending on the type of rubber,the particular methylene acceptor, the particular methylene donor andthe desired physical properties, i.e., adhesion and tear. Generallyspeaking, the amount of methylene acceptor may range from about 0.1 toabout 10 phr. Preferably, the amount of methylene acceptor ranges fromabout 0.5 to about 5.0 phr.

[0090] The abrasion resistant tread rubber 82A,B contains a methylenedonor which is suitable for reaction with the methylene acceptor.Examples of methylene donors which are suitable for use in the presentinvention include hexamethylenetetramine, hexaethoxymethylmelamine,hexamethoxymethylmelamine, lauryloxymethoxypyridinium chloride,ethoxymethylpyridinium chloride, trioxan hexamethoxymethylmelamine, thehydroxy groups of which may be esterified or partially esterified, andpolymers of the methylene donors may be N-substituted oxymethylmelaminesof the formula:

[0091] wherein X is an alkyl having from 1 to 8 carbon atoms, R, R₁, R₂,R₃, and R₄ are individually selected from the group consisting ofhydrogen, an alkyl having from 1 to 8 carbon atoms, the group —CH₂OX ortheir condensation products. Specific methylene donors includehexakis-(methoxymethyl)melamine,N,N′,N″-trimethyl/N,N′,N″-trimethylolmelamine, hexamethylolmelamine,N,N′,N″-dimethylolmelamine, N-methylolmelamine, N,N′-dimethylolmelamine,N,N′,N″-tris(methoxymethyl)melamine andN,N′N″-tributyl-N,N′,N″-trimethylol-melamine. The N-methylol derivativesof melamine are prepared by known methods.

[0092] The amount of methylene acceptor that is present in the abrasionresistant tread compound 82A,B may vary depending on the type of rubber,the particular methylene acceptor, the particular methylene donor andthe desired physical properties, i.e., adhesion and tear. Generallyspeaking, the amount of methylene donor may range from about 0.1 toabout 10 phr. Preferably, the amount of methylene donor ranges fromabout 0.5 to about 5.0 phr.

[0093] The weight ratio of methylene donor to methylene acceptor canvary. Generally speaking, the weight ratio will range from about 1:10 toabout 10:1. Preferably, the weight ratio ranges from about 1:3 to 3:1.

[0094] The term “phr” as used herein, and according to conventionalpractice, refers to “parts by weight of a respective material per 100parts by weight of rubber, or elastomer.”

[0095] It is readily understood by those having skill in the art thatthe abrasion resistant tread compound 82A,B would be compounded bymethods generally known in the rubber compounding art, such as mixingthe various sulfur-vulcanizable constituent rubbers with variouscommonly-used additive materials such as, for example, sulfur donors,curing aids, such as activators and retarders and processing additives,such as oils, resins including tackifying resins and plasticizers,fillers, pigments, fatty acid, zinc oxide, waxes, antioxidants andantiozonants and peptizing agents. As known to those skilled in the art,depending on the intended use of the sulfur vulcanizable andsulfur-vulcanized material (rubbers), the additives mentioned above areselected and commonly used in conventional amounts. Representativeexamples of sulfur donors include elemental sulfur (free sulfur), anamine disulfide, polymeric polysulfide and sulfur olefin adducts.Preferably, the sulfur-vulcanizing agent is elemental sulfur. Thesulfur-vulcanizing agent may be used in an amount ranging from 0.5 to 8phr, with a range of from 1.5 to 6 phr being preferred. The abrasionresistant tread compound 82A,B may include from about 0 to 15 phr ofsofteners including tackifier resins and processing oils. Typicalamounts of tackifier resins, if used, comprise about 0.5 to about 10phr, usually about 1 to about 5 phr. Typical amounts of processing oilscomprise about 1 to about 15 phr. Such processing oils can include, forexample, aromatic, naphthenic, and/or paraffinic processing oils.Typical amounts of antioxidants comprise about 1 to about 5 phr.Representative antioxidants may be, for example,diphenyl-p-phenylenediamine and others, such as, for example, thosedisclosed in The Vanderbilt Rubber Handbook (1978), Pages 344 through346. Typical amounts of antiozonants comprise about 1 to 5 phr. Typicalamounts of fatty acids, if used, which can include stearic acid compriseabout 0.5 to about 3 phr. Typical amounts of zinc oxide comprise about 2to about 5 phr. Typical amounts of waxes comprise about 1 to about 5phr. Often microcrystalline waxes are used. Typical amounts of peptizerscomprise about 0.1 to about 1 phr. Typical peptizers may be, forexample, pentachlorothiophenol and dibenzamidodiphenyl disulfide.

[0096] Accelerators are used in the abrasion resistant tread compound82A,B to control the time and/or temperature required for vulcanizationand to improve the properties of the vulcanizate. In one embodiment, asingle accelerator system may be used, i.e., primary accelerator. Theprimary accelerator(s) may be used in total amounts ranging from about0.5 to about 4, preferably about 0.8 to about 1.5, phr. In anotherembodiment, combinations of a primary and a secondary accelerator mightbe used with the secondary accelerator being used in smaller amounts,such as from about 0.05 to about 3 phr, in order to activate and toimprove the properties of the vulcanizate. Combinations of theseaccelerators might be expected to produce a synergistic effect on thefinal properties and are somewhat better than those produced by use ofeither accelerator alone. In addition, delayed action accelerators maybe used which are not affected by normal processing temperatures butproduce a satisfactory cure at ordinary vulcanization temperatures.Vulcanization retarders might also be used. Suitable types ofaccelerators that may be used in the present invention are amines,disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides,dithiocarbamates and xanthates. Preferably, the primary accelerator is asulfenamide. If a second accelerator is used, the secondary acceleratoris preferably a guanidine, dithiocarbamate or thiuram compound.

[0097] The mixing of in the abrasion resistant tread compound 82A,B canbe accomplished by methods known to those having skill in the rubbermixing art. For example the ingredients are typically mixed in at leasttwo stages, namely at least one non-productive stage followed by aproductive mix stage. The final curatives including sulfur-vulcanizingagents are typically mixed in the final stage which is conventionallycalled the “productive” mix stage in which the mixing typically occursat a temperature, or ultimate temperature, lower than the mixtemperature(s) than the preceding non-productive mix stage(s). The terms“non-productive” and “productive” mix stages are well known to thosehaving skill in the rubber mixing art. The rubber composition may besubjected to a thermomechanical mixing step. The thermomechanical mixingstep generally comprises a mechanical working in a mixer or extruder fora period of time suitable in order to produce a rubber temperaturebetween 140° C. and 190° C. The appropriate duration of thethermomechanical working varies as a function of the operatingconditions and the volume and nature of the components. For example, thethermomechanical working may be from 1 to 20 minutes.

[0098] Vulcanization of the tire assembly is generally carried out atconventional temperatures ranging from about 100° C. to 200° C.Preferably, the vulcanization is conducted at temperatures ranging fromabout 110° C. to 180° C. Any of the usual vulcanization processes may beused such as heating in a press or mold, heating with superheated steamor hot air. Such tires can be built, shaped, molded and cured by variousmethods which are known and will be readily apparent to those havingskill in such art.

[0099] The two-piece assembly offers better traction, wear, andfootprint, along with quicker field changeover and tire replacement. Inorder to deliver required tire durability in service, the abrasionresistant tread compound 82A,B must be of sufficient gauge toeliminate/reduce excessive rubbing which could lead to wire exposure.The compound formulation can consist of a mixture of diene rubbers,primarily polyisoprene, with secondary polymers of the SBR or PBD type,ranging from 20 to 50 phr. Fillers can be HAF or ISAF, with or withoutsilica fillers of 150 to 175 surface area. Also included can be aheat-reactive resin system, together with 4 to 6 phr aromatic processingoil. Compound physicals range from 4.6 to 11.5 MN/m², tensile-at-breakfrom 12 to 24 MN/m , and elongation range from 525 to 625 percent.Abrasion rates vary from 8.25 to 13.95 mg/km at 12 degree slip angle, 70N Load (Grosch abrasion tester).

EXAMPLE

[0100] In this Example, several rubber compounds were mixed and cured tobe tested for physical properties. Compound recipes for samples 1-5 aregiven in Table 1. Rubber compounds were mixed following standardtechniques and cured at 135° C. for 140 minutes. In addition to thecomponents listed, the compounds included standard amounts of curativesand antidegradants. Physical properties were measured for each curedcompound following standard test protocols. Results of physical propertytests are given in Table 2. TABLE 1 Sample Compound Recipes 1 2 3 4 5Natural Rubber 100 80 70 50 50 Styrene-Butadiene Rubber 0 20 30 0 0Polybutadiene 0 0 0 50 50 HAF Carbon Black 30 0 50 50 45 ISAF CarbonBlack 0 48 0 0 0 Silica 20 7 0 0 0 Resin 2.25 0 0 0 13 Oil 4 6 5 13 6

[0101] TABLE 2 Sample Physical Properties 1 2 3 4 5 300% Modulus, MPa9.3 7.3 10.7 12 5.3 Tensile Strength at Break, MPa 27 24.2 20 — 16.4Elongation at Break, % 620 670 485 460 680 Rebound, % 71.2 54.5 56.847.6 46.7 DIN abrasion 162 142 — 93 68 Peel Tear 182 161 92 83 126

What is claimed is:
 1. A two-piece tire assembly having a removabletread belt for installing about the circumference of a tire carcass anda tire carcass having an inflated and unloaded outer circumferentialsurface having an axial dimension no greater than the axial width of theremovable tread belt, the two-piece tire assembly being characterizedby: the carcass having a radially outermost and the tread belt having aradially innermost layer made of tread rubber, each tread rubber layerforming an abrasion resistance surface between the tread belt and thecarcass, the tread rubber comprising per 100 parts by weight ofelastomer (phr): from about 50 to about 100 phr of natural or syntheticpolyisoprene; from about 0 to about 20 phr of a polybutadiene; fromabout 0 to about 50 phr of a styrene-butadiene rubber; and from about 10to about 100 phr of a filler selected from carbon black and silica. 2.The two-piece tire assembly of claim 1, wherein said tread rubberfurther comprises from about 30 to about 70 phr of a filler selectedfrom carbon black and silica.
 3. The two-piece tire assembly of claim 1,wherein said tread rubber further comprises from about 0 to about 10 phrof a softener selected from tackifying resins and processing oils. 4.The two-piece tire assembly of claim 1, wherein said tread rubberfurther comprises from 0 to about 15 phr of a heat reactive resinsystem.
 5. The two-piece tire assembly of claim 1, wherein said treadrubber further comprises from about 0 to about 15 phr of a heat reactiveresin system comprising at least one methylene donor and at least onemethylene acceptor; said at least one methylene donor selected from thegroup consisting of hexamethylenetetramine, hexaethoxymethylmelamine,hexamethoxymethylmelamine, lauryloxymethoxypyridinium chloride,ethoxymethylpyridinium chloride, trioxan hexamethoxymethylmelamine, thehydroxy groups of which may be esterified or partially esterified, andpolymers of the methylene donors may be N-substituted oxymethylmelaminesof the formula:

wherein X is an alkyl having from 1 to 8 carbon atoms, R, R₁, R₂, R₃,and R₄ are individually selected from the group consisting of hydrogen,an alkyl having from 1 to 8 carbon atoms, the group —CH₂OX or theircondensation products; and said at least one methylene acceptor selectedfrom the group consisting of resorcinol, unmodified phenol novolakresins, modified phenol novolak resin, and resorcinol novolak resins. 6.The two-piece tire assembly of claim 1, wherein said tread rubber of thetread belt has a gauge of at least 0.1 inches.
 7. The two-piece tireassembly of claim 1, wherein said tread rubber of the tread belt has agauge of at least 0.3 inches.
 8. The two-piece tire assembly of claim 1,wherein said tread rubber has a modulus ranging from about 4.6 to about11.5 MN/m²; a tensile strength of from about 12 to about 24 MN/m²; andan elongation of from about 525 to about 625 percent.
 9. The two-piecetire assembly of claim 1, wherein said tread rubber has an abrasion rateof from about 8.25 to about 13.95 mg/km, measured at a 12 degree slipangle and a 70 N load.
 10. The two-piece tire assembly of claim 1wherein the tread belt has a rubber tread, the rubber tread materialbeing the same as the tread rubber layer of the carcass.
 11. Thetwo-piece tire assembly of claim 1, the tread belt having a pair oflateral ends each axially extending beyond the inflated unloaded carcassat the outer circumferential surface of the carcass by a distance of atleast 4% of carcass width as measured at the tread belt and carcassinterface and wherein the tread belt width is at best equal to or widerthan the loaded deflected carcass width as measured at the outercircumference of the carcass, each lateral end of the tread belt havinga plurality of circumferentially extending cords in a firstreinforcement layer and being radially inwardly flexible under load. 12.The two-piece tire assembly of claim 11 wherein the removable tread belthas a radially outer surface having a substantially flat tread arcradius R₁ between the lateral ends extending from 50% to 75% of thetread belt axial width and a smaller tread arc radius R₂ extending fromthe first tread arc R₁, the tread outer surface having a sloping surfaceextending from a tangency to R₂ to a lateral end, the radial differencein the tread belt surface as measured at the centerline of the treadbelt and each lateral end of the removable tread belt being greater than0.3% of the outside diameter as measured by the centerline of the treadbelt.
 13. The two-piece tire assembly of claim 11 wherein the removabletread belt further comprises a belt reinforcing structure radiallyoutward of the circumferentially extending cords in the firstreinforcement layer.
 14. The two-piece tire assembly of claim 13 whereinthe belt reinforcing structure has a pair of cross-plies and a radiallyouter ply having cords oriented substantially 90 relative to thecircumferentially extending cords in a first reinforcement layer.